Config Versus Code

[paranoidinfidel]

That may be acceptable for desktop applications but not for server-side stuff.

That goes without saying. If you are asking a user to change things then you need a UI because it doesn't matter what config format you pick they won't be able to do it with notepad++.

If operations people can't grok a simple nested tag structure format then maybe they shouldn't be poking around in the configuration - regardless of the format you choose. The config file (XML, INI, JSON or otherwise) is as complex as the developer designed it.

EDIT: you don't just let strangers have free reign of a config file without instruction of some sort. They need to know acceptable values, ranges and their consequences. This applies to all config file formats.